The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Internal combustion engines draw air into an intake manifold through an inlet system that may be regulated by a throttle. The air in the intake manifold may be distributed to a plurality of cylinders and combined with fuel to create an air/fuel (A/F) mixture. The fuel may be provided via a plurality of fuel injectors located at intake ports of the cylinders (i.e., port fuel injection) or in the cylinders (i.e., direct fuel injection). The A/F mixture may be compressed by pistons and combusted within the cylinders to drive the pistons and rotatably turn a crankshaft generating drive torque.
Homogeneous charge compression ignition (HCCI) engines may operate in a plurality of combustion modes depending on operating conditions (e.g., engine load). The plurality of combustion modes may include HCCI combustion, spark ignition (SI) combustion, and mixed-mode combustion (e.g., a combination of HCCI and SI combustion). More specifically, for example, HCCI engines may operate via mixed-mode combustion at low engine loads, HCCI combustion at medium engine loads, and SI combustion at high engine loads.
SI combustion includes compressing the A/F mixture and igniting the compressed A/F mixture via spark from spark plugs. HCCI combustion, on the other hand, includes compressing the A/F mixture until a critical pressure and/or temperature is reached and the A/F mixture automatically combusts. Mixed-mode combustion, as previously stated, includes a combination of HCCI combustion and SI combustion. More specifically, mixed-mode combustion includes HCCI combustion plus “assisting” the combustion of the A/F mixture via spark from spark plugs.